1. Field of the Invention
This invention relates to an image processing system and, more particularly, to an image processing system for processing and coding a plurality of moving pictures.
2. Description of the Related Art
When a plurality of images (here assumed to be two, represented by A and B) are combined and displayed in an image processing system of the type in which a subject of any desired shape in a plurality of moving pictures is cut out and displayed in combination with another image, mask information which designates the shape to be cut out is prepared for each and every frame to perform the combination of images. For example, mask data contained in the mask information comprises "0"s and "1"s, and the aforementioned images A and B are combined by executing processing in which, when the mask data of a certain pixel is "1", the data of the corresponding pixel in the image A is selected, and when the mask data of a certain pixel is "0", the data of the corresponding pixel in the image B is selected. The combined image data is capable of being stored in a frame memory or coded.
Several methods have been proposed with regard to the coding of a moving picture. A particularly useful method of moving-picture coding is a motion-compensating (MC) prediction method based upon detection of motion. Though many methods of detecting motion have been proposed, a motion-compensating prediction method using block matching will be described in brief.
First, a motion vector is obtained by searching for blocks (having similar luminance-value pattern) which will minimize the sum of the differences between blocks (e.g., 8.times.8 pixels) in an image of an n.sup.th frame, the search being performed in an image of the (n-1).sup.th frame. Next, by using the motion vector, a predicted image of the (n+1).sup.th frame is created from the image of the n.sup.th frame. A differential image between the predicted image and the input image of the (n+1).sup.th frame is then coded along with the motion vector. This method of coding is known as motion-compensating prediction coding.
However, in the example of the prior art described above, an enormous amount of time is required since the object to be combined with another image must be cut out every frame.
Furthermore, the motion detection processing in such moving-picture coding requires a great amount of calculation. For example, if block size in the block-matching method is 16.times.16, then 256 subtraction operations and 255 addition operations will be required in the processing for finding the block-by-block differential, and this processing must be executed for all searched areas (e.g., 32.times.32 areas). Moreover, there is the danger of obtaining erroneous motion information, in which a pixel in a certain area corresponds to a pixel in a different area.